|Solid state semiconductor device for amplifying, controlling, and generating electrical signals, and having at least three electrical contacts. A transistors acts as a variable valve which, based on its input current or input voltage, allows a precise amount of current to flow through it from the circuit's voltage supply. Transistors usually consist of three layers of semiconductor material, in which the flow of electric current across the outer layer is regulated by the voltage or current applied at the middle layer. Transistors can act on a signal to perform a variety of functions such as amplification, rectification, modulation or demodulation, and buffering. The transistor is the fundamental building block of modern electronic devices, and is universal in modern electronic systems.